Pure line populations of brown planthopper, Nilaparvata lugens (Ståi), are needed for identifying new genetic sources of resistance. Among the known N. lugens biotypes in the Philippines, Biotype 1 can infest rice cultivare which lack genes for resistance. Biotype 2 can damage cultivars carrying Bph1 resistance gene, in addition to those that are susceptible to Biotype 1. Biotype 3 can infest rice cultivars carrying bph2 resistance gene, in addition to those susceptible to Biotype 1. In the greenhouse Biotypes 1, 2, and 3 are maintained on TN1 (no resistance gene), Mudgo (Bph1 gene) and ASD7 (bph2 gene) rice plants, respectively. Because Biotype 1 population is reared on TN1 plants, susceptible to all the three biotypes, accidental infestations of Biotype 1, Biotype 2 and Biotype 3 cannot be ruled out.

N. lugens biotypes were separated from each other by their differential ingestion and assimilation of food on different susceptible and resistant rice cultivars. A homogeneous population of Biotype 1 of N. lugens was produced from single pairs of males and females selected on the basis of their low food intake on rice cultivars Mudgo and ASD7. The purity of such Biotype 1 population was further demonstrated for three generations based on differential nymphal growth and development and adult longevity and fecundity on resistant Mudgo and ASD7 and on the susceptible TN1 rice cultivars. The technique can also be useful in identifying biotypes of other sucking insect pests.

Insect pests are major yield reducers in sorghum under traditional farming practices in Africa. The use of resistant varieties in an integrated pest management scheme provides the most cost effective and practical means of sorghum insect control. Corneous grain sorghums are more weevil resistant than their softer endosperm counterparts. A wide range of sources of resistance to shootfiy, stem-borer and greenbug are known. Breeding for resistance to sorghum insects has been practised with varying degrees of success. Greenbug resistance breeding in sorghum has been successful in the U.S.A. Stem-borers are perhaps the most serious group of sorghum insects in Eastern Africa and further efforts are needed in breeding for resistance to these pests. In an effective pest resistance breeding work, the breeder and the entomologist must work as a team to make the fastest possible progress. Where several pests are of concern in an area, genotypes with multiple resistance in good agronomic backgrounds are needed.